Re: [PATCH] drm/dp: For MST hub, Get max_link_rate&max_lane from extended rx capability field if EXTENDED_RECEIVER_CAPABILITY_FILED_PRESENT is set.

[Koba Ko]

On Thu, Aug 27, 2020 at 1:30 PM Koba Ko <koba.ko@xxxxxxxxxxxxx> wrote:
>
> Currently, DRM get the capability of the mst hub only from DP_DPCD_REV and
> get the slower speed even the mst hub can run in the faster speed.
>
> As per DP-1.3, First check DP_EXTENDED_RECEIVER_CAP_FIELD_PRESENT.
> If DP_EXTENDED_RECEIVER_CAP_FIELD_PRESENT is 1, read the DP_DP13_DPCD_REV to
> get the faster capability.
> If DP_EXTENDED_RECEIVER_CAP_FIELD_PRESENT is 0, read DP_DPCD_REV.
>
> Signed-off-by: Koba Ko <koba.ko@xxxxxxxxxxxxx>
> ---
>  drivers/gpu/drm/drm_dp_mst_topology.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
> index 67dd72ea200e..3b84c6801281 100644
> --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> @@ -3497,6 +3497,8 @@ static int drm_dp_get_vc_payload_bw(u8 dp_link_bw, u8  dp_link_count)
>  int drm_dp_mst_topology_mgr_set_mst(struct drm_dp_mst_topology_mgr *mgr, bool mst_state)
>  {
>         int ret = 0;
> +       u8 dpcd_ext = 0;
> +       unsigned int dpcd_offset = 0;
>         struct drm_dp_mst_branch *mstb = NULL;
>
>         mutex_lock(&mgr->payload_lock);
> @@ -3510,9 +3512,15 @@ int drm_dp_mst_topology_mgr_set_mst(struct drm_dp_mst_topology_mgr *mgr, bool ms
>                 struct drm_dp_payload reset_pay;
>
>                 WARN_ON(mgr->mst_primary);
> +               drm_dp_dpcd_read(mgr->aux,
> +                                DP_TRAINING_AUX_RD_INTERVAL,
> +                                &dpcd_ext, sizeof(dpcd_ext));
> +
> +               dpcd_offset =
> +                       ((dpcd_ext & DP_EXTENDED_RECEIVER_CAP_FIELD_PRESENT) ?  DP_DP13_DPCD_REV : DP_DPCD_REV);
>
>                 /* get dpcd info */
> -               ret = drm_dp_dpcd_read(mgr->aux, DP_DPCD_REV, mgr->dpcd, DP_RECEIVER_CAP_SIZE);
> +               ret = drm_dp_dpcd_read(mgr->aux, dpcd_offset, mgr->dpcd, DP_RECEIVER_CAP_SIZE);
>                 if (ret != DP_RECEIVER_CAP_SIZE) {
>                         DRM_DEBUG_KMS("failed to read DPCD\n");
>                         goto out_unlock;
> --
> 2.25.1
>
Add Lyude Paul